Atomic oscillator

ABSTRACT

An atomic oscillator includes a gas cell that has metal atoms sealed therein, a heating unit that heats the gas cell, a heat transmission unit that is positioned between the gas cell and the heating unit, is thermally connected to the gas cell, and transmits heat generated by the heating unit to the gas cell, and a light absorbing unit that is thermally connected to the gas cell so as to be separated from the heat transmission unit and absorbs heat of the gas cell. The heat transmission unit includes a gas cell accommodation portion including at least a pair of gas cell accommodation walls disposed outside the gas cell, and a thermal conductive elastic member which is interposed in a gap formed by the gas cell and the gas cell accommodation walls of the heat transmission unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/283,742, filed on Oct. 3, 2016, which claims the benefit of JapanesePatent Application No. 2015-198261, filed on Oct. 6, 2015. Thedisclosures of the above applications are hereby incorporated byreference herein in their entireties.

BACKGROUND 1. Technical Field

The present invention relates to an atomic oscillator.

2. Related Art

As an oscillator having high-accuracy oscillation characteristics on along-term basis, an atomic oscillator is known which oscillates on thebasis of energy transfer of atoms of an alkali metal such as rubidium orcesium. In general, an operating principle of the atomic oscillator isclassified broadly into a method using a double resonance phenomenonbased on light and microwaves and a method using a quantum interferenceeffect (CPT: coherent population trapping) based on two types of lightbeams having different wavelengths.

In any type of atomic oscillator, an alkali metal is sealed in a gascell together with a buffer gas, and the gas cell is required to beheated to a predetermined temperature by a heater in order to maintainthe alkali metal in a gaseous state. Here, in general, the alkali metalwithin the gas cell partially changes to liquid as a surplus portionwithout being wholly gasified. Such surplus alkali metal atoms change toliquid by separating (condensing) out to a low temperature portion ofthe gas cell. However, when the alkali metal atoms are present in aregion through which excitation light passes, the atoms shield theexcitation light, which results in a deterioration in oscillationcharacteristics of the atomic oscillator.

Consequently, in a gas cell disclosed in JP-A-2007-324818, a concaveportion for separating an alkali metal is provided at a position awayfrom an optical axis of excitation light. A portion apart from theconcave portion of the gas cell is heated by a heater, thereby makingthe temperature of the concave portion lower than that of the peripheralportion thereof. Thus, a surplus portion of the alkali metal is storedin the concave portion as liquid, which preventing the surplus portionfrom shielding the excitation light.

However, in a case where the atomic oscillator disclosed inJP-A-2007-324818 is made small, heat generated by the heater istransmitted to the entire atomic oscillator depending on the size of theatomic oscillator. For this reason, even the temperature of the concaveportion rises. As a result, the surplus portion of the alkali metal isnot stored in the concave portion as liquid, and thus there is thepossibility of the surplus portion shielding the excitation light. Inthis manner, it is difficult to partially change the temperature of thegas cell of the atomic oscillator which is reduced in size.

JP-A-2015-122597 discloses a quantum interference device which isincluded in an atomic oscillator. The quantum interference devicedisclosed in JP-A-2015-122597 includes a heating unit that transmitsheat, which is supplied from the heating unit, to a gas cell and a heatradiation unit that forms a low temperature portion in the gas cell,thereby preventing a surplus portion of an alkali metal from condensingon a path through which excitation light passes. Therefore, it ispossible to obtain the quantum interference device with highreliability.

In the quantum interference device disclosed in JP-A-2015-122597, heatmovement (heat transmission) is performed in the heating unit connectedto the gas cell or the heat radiation unit due to a close contactbetween the gas cell and a connection portion. However, as is wellknown, so-called “variations in dimensions” occur at the time ofmanufacturing a component. Variations also occur in a gap between thegas cell and the heating unit or a gap between the gas cell and the heatradiation unit due to the variations in dimensions. For example, whenthe gap becomes larger, an air layer formed in the gap serves as a heatinsulating layer, which remarkably degrading the efficiency of heatingor heat radiation of the gas cell. In particular, the degradation in theefficiency of heat transmission in the heating unit destabilizes thetemperature of the gas cell, thereby reducing the reliability of thequantum interference device. Alternatively, in a state where componentsoverlap each other without a gap formed therebetween and interfere witheach other, a large load is applied to a glass gas cell, which leads toa concern that the gas cell may be damaged or broken.

SUMMARY

An advantage of some aspects of the invention is to provide an atomicoscillator that prevents a gas cell from being damaged in spite of theoccurrence of variations in dimensions and has a high operationalstability without impairing the efficiency of heat transmission from aheating unit to the gas cell.

The invention can be implemented as the following forms or applicationexamples.

Application Example 1

An atomic oscillator according to this application example includes agas cell that has metal atoms sealed therein, a heating unit that heatsthe gas cell, a heat transmission unit that is positioned between thegas cell and the heating unit, is thermally connected to the gas cell,and transmits heat generated by the heating unit to the gas cell, and alight absorbing unit that is thermally connected to the gas cell so asto be separated from the heat transmission unit and absorbs heat of thegas cell. The heat transmission unit includes a gas cell accommodationportion including gas cell accommodation walls disposed outside the gascell, and a thermal conductive elastic member which is interposed in agap formed by the gas cell and the gas cell accommodation walls of theheating unit.

According to the atomic oscillator of this application example, it ispossible to effectively form a low temperature portion having atemperature lower than that of a peripheral portion thereof even in agas cell which is reduced in size. Accordingly, it is possible tocondense metal atoms in the low temperature portion and to store asurplus portion as liquid. In this manner, the surplus portion can beeasily controlled, and thus it is possible to easily prevent the surplusportion from shielding a light path of excitation light and to increasethe reliability of a quantum interference device.

Further, a reduction in the size of the gas cell leads to a reduction inthe thickness of a material constituting the gas cell, and thus it isnecessary to provide a gap between the gas cell and the gas cellaccommodation wall of the heat transmission unit in order to avoid thedamage of the gas cell which is caused by interference betweencomponents due to manufacturing variations of the gas cell accommodationwall and the gas cell. However, the gap between the gas cellaccommodation wall and the gas cell serves as a region in which gas suchas air is present, and thus the performance of heat transmission fromthe gas cell accommodation wall to the gas cell is degraded.Consequently, it is possible to secure a heat transmission path from thegas cell accommodation wall to the gas cell by disposing the thermalconductive elastic member in the gap between the gas cell accommodationwall and the gas cell and to stably fix the gas cell between the gascell accommodation walls by elasticity of the thermal conductive elasticmember.

Application Example 2

In the application example, the thermal conductive elastic member may bea rubber-based adhesive, a packing, or a sheet piece.

According to this application example, it is possible to dispose the gascell within the gas cell accommodation walls and to then easily disposethe thermal conductive elastic member in the gap formed between the gascell accommodation wall and the gas cell.

Application Example 3

In the application example, the thermal conductive elastic member may bea rubber-based filler.

According to this application example, it is possible to dispose the gascell within the gas cell accommodation walls and to then easily disposethe fillable thermal conductive elastic member in the gap by fillingeven when variations occur in the gap formed between the gas cellaccommodation wall and the gas cell.

Application Example 4

In the application example, the atomic oscillator may further include acoil that generates a magnetic field passing through the gas cell, and amagnetic shield that accommodates the gas cell, the heat transmissionunit, the light absorbing unit, and the coil therein, the heattransmission unit and the light absorbing unit may be thermallyconnected to the magnetic shield, and the heating unit may be thermallyconnected to an outside of the magnetic shield.

According to this application example, it is possible to generate amagnetic field passing through the gas cell by electrifying the coil andto improve a resolution by widening a gap between different energylevels at which the atoms of an alkali metal present within the gas celldegenerate by Zeeman splitting, thereby allowing a line width of anelectromagnetically induced transparency (EIT) signal to be reduced. Inorder to stabilize the magnetic field generated from the coil, amagnetic shield, other than the coil, for preventing a line of magneticforce from the outside from being infiltrated into the gas cell isprovided.

In addition, the heating unit, the heat transmission unit, and the lightabsorbing unit are thermally connected to a magnetic shield connected tothe air, and thus it is possible to diffuse heat generated by theheating unit from a connection portion between the heating unit and themagnetic shield in a wide range along the shape of the magnetic shieldand to transmit a larger amount of light beams to the heat transmissionunit. On the other hand, the light absorbing unit is thermally connectedto the magnetic shield, and thus it is possible to form a wide region inwhich heat is radiated to the air in the magnetic shield and toeffectively radiate heat transmitted to the light absorbing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram showing a schematic configuration of an atomicoscillator according to a first embodiment.

FIG. 2 is a diagram showing an energy state of an alkali metal.

FIG. 3 is a graph showing a relationship between intensity of lightdetected by a light detection unit and a frequency difference betweentwo light beams emitted from a light emission unit.

FIG. 4 is a schematic perspective view showing the atomic oscillatoraccording to the first embodiment.

FIG. 5 is a cross-sectional view of a second unit included in the atomicoscillator according to the first embodiment.

FIG. 6 is a perspective view of a heat transmission unit shown in FIG.5.

FIG. 7 is a cross-sectional view of a portion taken along line A-A′shown in FIG. 5.

FIG. 8 is a perspective view of a light absorbing unit shown in FIG. 5.

FIG. 9 is a cross-sectional view of a portion taken along line B-B′shown in FIG. 5.

FIG. 10 is a schematic diagram showing inner temperature distribution ofa gas cell included in the atomic oscillator according to the firstembodiment.

FIG. 11 is a cross-sectional view showing another configuration of aheat transmission member of the atomic oscillator according to the firstembodiment.

FIG. 12 is a cross-sectional view showing another configuration of theheat transmission member of the atomic oscillator according to the firstembodiment.

FIG. 13 is a cross-sectional view showing another configuration of theheat transmission member of the atomic oscillator according to the firstembodiment.

FIG. 14 is a cross-sectional view showing another configuration of theheat transmission member of the atomic oscillator according to the firstembodiment.

FIG. 15 is a diagram showing a schematic configuration of a positioningsystem using a GPS satellite as an example of an electronic apparatusaccording to a second embodiment.

FIG. 16 is a schematic diagram showing a configuration of a clocktransmission system as an example of an electronic apparatus accordingto a third embodiment.

FIG. 17 is a perspective view showing a configuration of a vehicle as anexample of a moving object according to a fourth embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments according to the invention will be describedwith reference to the accompanying drawings.

First Embodiment

FIG. 1 is a diagram showing a schematic configuration of an atomicoscillator according to a first embodiment. In addition, FIG. 2 is adiagram showing an energy state of an alkali metal, and FIG. 3 is agraph showing a relationship between intensity of light detected by alight detection unit and a frequency difference between two light beamsemitted from a light emission unit.

An atomic oscillator 100 shown in FIG. 1 is an atomic oscillator using aquantum interference effect. As shown in FIG. 1, the atomic oscillator100 includes a first unit 200 which is a unit on the light emissionside, a second unit 300 which is a unit on the light detection side, anda control unit 400 that controls the first unit 200 and the second unit300.

The first unit 200 includes a light emission device 210 and an opticalcomponent group 220. The light emission device includes a light emissionunit 211 and a first package 212 that accommodates the light emissionunit 211 and includes a window portion 213 transmitting light. Inaddition, the second unit 300 includes a gas cell 310, a light detectionunit 320, a coil 350, a heater 330 as a heating unit, a temperaturesensor 340, a heat transmission unit to be described later, a lightabsorbing unit, and a magnetic shield that accommodates thesecomponents.

First, the principle of the atomic oscillator 100 will be brieflydescribed. As shown in FIG. 1, in the atomic oscillator 100, the lightemission unit 211 emits an excitation light LL toward the gas cell 310,and the excitation light LL passing through the gas cell 310 is detectedby the light detection unit 320. A gaseous alkali metal (metal atoms) issealed in the gas cell 310. As shown in FIG. 2, the alkali metal has anenergy level of a three-level system, and can take three states of twoground states (ground states 1 and 2) having different energy levels andan excited state. Here, the ground state 1 is an energy state which islower than the ground state 2.

The excitation light LL emitted from the light emission unit 211includes two types of resonance light beams 1 and 2 having differentfrequencies. When the above-described gaseous alkali metal is irradiatedwith the two types of resonance light beams 1 and 2, the lightabsorptivity (light transmittance) of the resonance light beams 1 and 2in the alkali metal changes in accordance with a difference (ω1−ω2)between a frequency ω1 of the resonance light beam 1 and a frequency ω2of the resonance light beam 2. When the difference (ω1−ω2) between thefrequency ω1 of the resonance light beam 1 and the frequency ω2 of theresonance light beam 2 is coincident with a frequency equivalent to anenergy difference between the ground state 1 and the ground state 2,excitation to the excited state from each of the ground states 1 and 2is stopped. At this time, both the resonance light beams 1 and 2 passwithout being absorbed into the alkali metal. Such a phenomenon isreferred to as a CPT phenomenon or an electromagnetically inducedtransparency (EIT) phenomenon.

For example, when the difference (ω1−ω2) between the frequency ω1 of theresonance light beam 1 and the frequency ω2 of the resonance light beam2 is coincident with a frequency ω0 equivalent to an energy differencebetween the ground state 1 and the ground state 2 in a case where thelight emission unit 211 fixes the frequency ω1 of the resonance lightbeam 1 and changes the frequency ω2 of the resonance light beam 2, thedetection intensity of the light detection unit 320 sharply increases asshown in FIG. 3. Such a sharp signal is detected as an EIT signal. TheEIT signal has an eigen value which is determined in accordance with thetype of alkali metal. Therefore, it is possible to configure anoscillator by using such an EIT signal.

Hereinafter, a specific configuration of the atomic oscillator 100 ofthis embodiment will be described. FIG. 4 is a schematic perspectiveview showing the atomic oscillator 100 shown in FIG. 1, and FIG. 5 is across-sectional view of the second unit 300 included in the atomicoscillator 100 shown in FIG. 1. In FIG. 5, for convenience ofdescription, an X-axis, a Y-axis, and a Z-axis are shown as three axesperpendicular to each other. A distal end side of each arrow shown inthe drawing is set to a “+(positive) side” and a base end side is set tobe a “− (negative) side”. In addition, hereinafter, for convenience ofdescription, a direction along the X-axis is referred to as an “X-axisdirection”, a direction along the Y-axis is referred to as a “Y-axisdirection”, and a direction along the Z-axis is referred to as a “Z-axisdirection”.

As shown in FIG. 4, the atomic oscillator 100 includes the first unit200, the second unit 300, and the control unit 400 (not shown in FIG. 4.See FIG. 1). The first unit 200 and the second unit 300 are electricallyconnected to the control unit 400 through a wiring and a connector (notshown), and the driving thereof is controlled by the control unit 400.

The first unit 200 includes the light emission device 210 and theoptical component group 220. The light emission device includes thelight emission unit 211, the first package 212 accommodating the lightemission unit 211, and the window portion 213.

The light emission unit 211 has a function of emitting the excitationlight LL for exciting the alkali metal atoms in the gas cell 310.Specifically, the light emission unit 211 is used to emit light, whichincludes the above-described two types of light beams (the resonancelight beam 1 and the resonance light beam 2) having differentfrequencies, as the excitation light LL. The frequency ω1 of theresonance light beam 1 is capable of exciting (resonating) the alkalimetal in the gas cell 310 to an excited state from the above-describedground state 1. In addition, the frequency ω2 of the resonance lightbeam 2 is capable of exciting (resonating) the alkali metal in the gascell 310 to an excited state from the above-described ground state 2.

The light emission unit 211 is not particularly limited as long as theunit is capable of emitting the above-described excitation light LL, buta semiconductor laser such as a vertical cavity surface emitting laser(VCSEL) can be used as the unit. In addition, the temperature of thelight emission unit 211 is adjusted to a predetermined temperature usinga temperature adjusting element (a heating resistor, a Peltier element,or the like) not shown in the drawing.

The first package 212 accommodates the light emission unit 211 mentionedabove. For example, as shown in FIG. 4, the first package 212 isconstituted by a housing having an external shape being a block shape.In addition, for example, a plurality of leads (not shown) protrude fromthe first package 212 and are electrically connected to the lightemission unit 211 through wirings. The leads are electrically connectedto a wiring board using a connector not shown in the drawing, or thelike. For example, a flexible substrate or a connector having a socketshape can be used as the connector. In addition, a wall portion of thefirst package 212 on the second unit 300 side is provided with thewindow portion 213. The window portion 213 is provided on an opticalaxis (axis a of the excitation light LL) between the gas cell 310 andthe light emission unit 211. The window portion 213 has lighttransmittance with respect to the excitation light LL mentioned above.

In this embodiment, the window portion 213 is a lens. Thereby, it ispossible to irradiate the gas cell 310 with the excitation light LLwithout waste. In addition, the window portion 213 has a function ofmaking the excitation light LL into parallel light. That is, the windowportion 213 is a collimate lens, and the excitation light LL in aninternal space S of the gas cell 310 to be described later is parallellight. Thereby, it is possible to increase the number of alkali metalatoms resonating by the excitation light LL emitted from the lightemission unit 211 among alkali metal atoms which are present in theinternal space S. As a result, it is possible to increase the intensityof an EIT signal.

Meanwhile, the window portion 213 is not limited to a lens as long as itis a portion having light transmittance with respect to the excitationlight LL. For example, the window portion may be an optical componentother than a lens, or may be a simple light transmissive plate-shapedmember. In this case, a lens having the above-described function may beprovided between the first package 212 and a magnetic shield 380 to bedescribed later similar to, for example, optical components 221, 222,and 223 constituting the optical component group 220 to be describedlater. A constituent material of a portion of the first package 212other than the window portion 213 is not particularly limited. Forexample, ceramics, a metal, or a resin can be used as the constituentmaterial.

In addition, in a case where a portion of the first package 212 otherthan the window portion 213 is formed of a material having lighttransmittance with respect to the excitation light LL, it is possible tointegrally form the window portion 213 and the portion of the firstpackage 212 other than the window portion 213. Meanwhile, in a casewhere the portion of the first package 212 other than the window portion213 is formed of a material that does not have light transmittance withrespect to the excitation light LL, the window portion 213 and theportion of the first package 212 other than the window portion 213 maybe formed as separate bodies and may be bonded to each other using aknown bonding method.

In addition, it is preferable that the inside of the first package 212is an airtight space. Thereby, it is possible to set the inside of thefirst package 212 to be in a decompression state or a state where aninert gas is sealed. As a result, it is possible to improve thecharacteristics of the atomic oscillator 100. In addition, a temperatureadjusting element or a temperature sensor which adjusts the temperatureof the light emission unit 211 may be accommodated in the first package212 (not shown). Examples of the temperature adjusting element include aheating resistor (heater), a Peltier element, and the like. According tothe first package 212, it is possible to accommodate the light emissionunit 211 in the first package 212 while allowing the emission of theexcitation light LL to the outside of the first package 212 from thelight emission unit 211.

The second unit 300 includes the magnetic shield 380, which accommodatesthe above-described gas cell 310, the light detection unit 320, the coil350, a heat transmission unit 360, and a light absorbing unit 370, theheater 330, and the temperature sensor 340.

An alkali metal such as gaseous rubidium, cesium, or sodium is sealed inthe gas cell 310. In addition, a rare gas such as argon or neon and aninert gas such as nitrogen may be sealed as a buffer gas in the gas cell310 together with an alkali metal gas, when necessary.

As shown in FIG. 5, the gas cell 310 included in the atomic oscillator100 according to this embodiment includes a main body 311 having athrough hole 311 a, and a pair of window portions 312 and 313 as lighttransmitting portions that close both openings of the both sides of thethrough hole 311 a and include a transmission region through which theexcitation light LL can pass. Thereby, the above-described internalspace S having an alkali metal sealed therein is formed. In addition, aprotrusion portion 311 b protruding outwards is formed in a portion ofthe main body 311, and the inside of the protrusion portion 311 bfunctions as a liquid reserving portion 311 c. The liquid reservingportion 311 c is a portion in which a portion of an alkali metal isstored in a liquid phase as a surplus portion. As described later, thetemperature of the liquid reserving portion 311 c is made lower than thetemperature of the peripheral portion thereof, and thus it is possibleto store the surplus portion of the alkali metal in the liquid reservingportion 311 c with the surplus portion being condensed.

A material constituting the main body 311 is not particularly limited,but includes a metal material, a resin material, a glass material, asilicon material, quartz crystal, and the like. From the viewpoint ofprocessability and bonding between the window portions 312 and 313, aglass material and a silicon material are preferably used. The windowportions 312 and 313 are airtightly bonded to such a main body 311.Thus, it is possible to make the internal space S of the gas cell 310into an airtight space.

A method of bonding the main body 311 and the window portions 312 and313 is determined in accordance with the constituent materials thereof,and is not particularly limited. For example, a bonding method using anadhesive, a direct bonding method, and an anodic bonding method can beused as the method. In addition, a material constituting the windowportions 312 and 313 is not particularly limited as long as the materialhas light transmittance with respect to the excitation light LLmentioned above. From the viewpoint of bonding to the main body 311,examples of the material include a silicon material, a glass material,quartz crystal, and the like, and the same material as that of the mainbody 311 is preferably used.

The window portions 312 and 313 have light transmittance with respect tothe excitation light LL from the light emission device 210 mentionedabove. One window portion 312 transmits the excitation light LL enteringthe gas cell 310, and the other window portion 313 transmits theexcitation light LL emitted from the gas cell 310. The gas cell 310 isheated by the heater 330, and the temperature thereof is adjusted to apredetermined temperature.

The light detection unit 320 has a function of detecting the intensityof the excitation light LL (resonance light beams 1 and 2) passingthrough the gas cell 310. The light detection unit 320 is notparticularly limited as long as the unit is a unit capable of detectingthe above-described excitation light LL. For example, a photodetector(light-receiving element) such as a solar cell or a photodiode can beused. In addition, the light detection unit 320 is accommodated in themagnetic shield 380 in this embodiment, but may be provided outside themagnetic shield 380. In this case, a window portion transmitting theexcitation light LL having passed through the gas cell 310 is formed inthe magnetic shield 380.

The coil 350 generates a magnetic field in a direction along the opticalaxis a of the excitation light LL in the internal space S by electricalconduction, and improves a resolution by widening a gap betweendifferent energy levels at which the atoms of the alkali metal withinthe internal space S degenerate by Zeeman splitting, thereby allowing aline width of an EIT signal to be reduced. Meanwhile, the magnetic fieldgenerated by the coil 350 may be any of a DC magnetic field and an ACmagnetic field, or may be a magnetic field in which a DC magnetic fieldand an AC magnetic field are superimposed on each other. The coil 350 isnot particularly limited. For example, the coil may be wound around theouter circumference of the gas cell 310 so as to configure a solenoidtype, or a pair of coils may face each other through the gas cell 310 soas to configure a Helmholtz type. In this embodiment, the coil 350 isconfigured as a solenoid type, and is wound around the heat transmissionunit 360, the gas cell 310, and the light absorbing unit 370. The coil350 is electrically connected to a magnetic field control unit 430 ofthe control unit 400 to be described later through a wiring not shown inthe drawing, and the coil 350 is electrified.

The magnetic shield 380 is constituted by a housing having an externalshape being a block shape, and accommodates the coil 350, the heattransmission unit 360, the gas cell 310, and the light absorbing unit370 therein. The magnetic shield 380 has a magnetic shielding propertyand has a function of shielding the gas cell 310 from an externalmagnetic field. Thereby, it is possible to stabilize a magnetic fieldgenerated by the coil 350 in the magnetic shield 380. Accordingly, it ispossible to achieve an improvement in the oscillation characteristics ofthe atomic oscillator 100.

In addition, a window portion 380 a is provided in a wall portion of themagnetic shield 380 on the first unit 200 side so as to penetrate thewall portion in the thickness direction thereof, and the excitationlight LL emitted from the light emission device 210 is incident on thegas cell 310 through the window portion 380 a. Meanwhile, a materialhaving a magnetic shielding property is used as the constituent materialof the magnetic shield 380. Examples of the constituent material includesoft magnetic materials such as Fe and various iron-based alloys(silicon iron, permalloy, amorphous, sendust, and Kovar). Among these,an Fe—Ni based alloy such as Kovar or permalloy is preferably used fromthe viewpoint of an excellent magnetic shielding property. In addition,a plurality of leads (not shown) electrically connected to the lightdetection unit 320, the heater 330, the temperature sensor 340 (notshown), and the coil 350 protrude from the magnetic shield 380, and theplurality of leads are electrically connected to a wiring board using aconnector not shown in the drawing, or the like through wirings.Examples of the connector to be used include a flexible substrate, aconnector having a socket shape, and the like.

The heater 330 has a function of heating an alkali metal which isairtightly sealed in the gas cell 310 mentioned above. Thereby, it ispossible to maintain the alkali metal in the gas cell 310 to a gaseousstate having a desired concentration. The heater 330 is heated byelectrical conduction. For example, the heater is constituted by aheating resistor provided on the outer surface of the gas cell 310. Sucha heating resistor is formed using, for example, a chemical vapordeposition (CVD) such as a plasma CVD or a thermal CVD, a dry platingmethod such as vacuum deposition, or a sol-gel method. Meanwhile, in acase where the heating resistor is provided on an incidence unit side oran emission unit side of the excitation light LL of the gas cell 310,the heating resistor is constituted by a material having lighttransmittance with respect to the excitation light LL, for example, atransparent electrode material such as an oxide, for example, indium tinoxide (ITO), indium zinc oxide (IZO), In₃O₃, SnO₂, SnO₂ containing Sb,or ZnO containing Al.

In addition, the heater 330 is connected to the magnetic shield 380 onthe outer side of the magnetic shield 380 through a heat transmissionplate 390 having a thermal conductivity higher than that of the magneticshield 380. As described above, since the heater 330 generates heat byelectrical conduction, a magnetic field is generated during the heatgeneration. However, the heater 330 is provided outside the magneticshield 380, and thus it is possible to prevent the magnetic fieldgenerated from the heater 330 from being infiltrated into the magneticshield 380 and to suppress influence on the magnetic field generatedfrom the coil 350.

Meanwhile, the heater 330 is not particularly limited as long as theheater is a heater capable of heating the gas cell 310, and may not comeinto contact with the gas cell 310. In addition, the gas cell 310 may beheated using a Peltier element instead of the heater 330 or inconjunction with the heater 330. The heater 330 is electricallyconnected to the temperature control unit 420 of the control unit 400 tobe described later, and thus the electrical conduction thereof iscontrolled.

Although not shown in FIG. 5, the atomic oscillator 100 includes thetemperature sensor 340. The temperature sensor 340 detects thetemperature of the heater 330 or the gas cell 310. The amount ofelectrical conduction to the heater 330 is controlled by the temperaturecontrol unit 420 (see FIG. 1) on the basis of detection results of thetemperature sensor 340, and the temperature of the heater 330 iscontrolled. The gas cell 310 is maintained to a desired temperature, andthus it is possible to maintain the temperature of the alkali metalatoms in the gas cell 310 to a desired temperature. Meanwhile, aninstallation position of the temperature sensor 340 is not particularlylimited. For example, the temperature sensor may be installed on theheater 330 or may be installed on the outer surface of the gas cell 310.The temperature sensor 340 is not particularly limited, and varioustypes of temperature sensors such as a thermistor or a thermocouple canbe used as the temperature sensor.

The first unit 200 includes the optical component group 220 constitutedby the plurality of optical components 221, 222, and 223. The opticalcomponent group 220 is provided on the optical axis a of the excitationlight LL between the gas cell 310 and the light emission unit 211 in thefirst package 212.

The optical component group 220 of this embodiment is configured suchthat the optical component 221, the optical component 222, and theoptical component 223 are disposed in this order toward the gas cell 310from the light emission unit 211. The optical component 221 is a λ/4wavelength plate. Thereby, for example, the excitation light LL which islinear polarized light from the light emission unit 211 can be convertedinto circularly polarized light (right circularly polarized light orleft circularly polarized light).

As described above, if alkali metal atoms within the gas cell 310 areirradiated with the excitation light LL which is linearly polarizedlight in a state where Zeeman splitting of the alkali metal atoms occursdue to a magnetic field of the coil 350 mentioned above, a plurality oflevels of the alkali metal atoms having been subjected to Zeemansplitting are uniformly dispersed by interaction between the excitationlight LL and the alkali metal atoms. As a result, the number of alkalimetal atoms having a desired energy level becomes relatively smallerthan the number of alkali metal atoms having other energy levels. Thus,the number of atoms expressing a desired EIT phenomenon is reduced, anda desired EIT signal becomes small. As a result, the oscillationcharacteristics of the atomic oscillator 100 are degraded.

On the other hand, as described above, when the alkali metal atomswithin the gas cell 310 are irradiated with the excitation light LLwhich is circularly polarized light in a state where Zeeman splitting ofthe alkali metal atoms occurs due to a magnetic field of the coil 350mentioned above, it is possible to make the number of alkali metal atomshaving a desired energy level relatively larger than the number ofalkali metal atoms having other energy levels among a plurality oflevels of the alkali metal atoms having been subjected to Zeemansplitting, by interaction between the excitation light LL and the alkalimetal atoms. For this reason, the number of atoms expressing a desiredEIT phenomenon is increased, and a desired EIT signal becomes large. Asa result, it is possible to improve the oscillation characteristics ofthe atomic oscillator 100.

Meanwhile, the plan-view shape of the optical component 221 is notlimited thereto, and may be a polygonal shape such as, for example, acircular shape, a quadrilateral shape, or a pentagonal shape. Inaddition, the optical component group 220 is configured such that theoptical components 222 and 223 are disposed on the second unit 300 sidein addition to the optical component 221. Each of the optical components222 and 223 is a neutral density filter (ND filter), and can reduce andadjust the intensity of the excitation light LL incident on the gas cell310. Accordingly, even when an output of the light emission unit 211 islarge, it is possible to set the amount of excitation light LL incidenton the gas cell 310 to a desired amount. Meanwhile, each of the opticalcomponents 222 and 223 has a plate shape. In addition, the shape of eachof the optical components 222 and 223 when seen in a plan view is notparticularly limited, and may be a polygonal shape such as, for example,a circular shape, a quadrilateral shape, or a pentagonal shape. Inaddition, either one or both of the optical components 222 and 223 maybe omitted depending on the magnitude of the output of the lightemission unit 211.

The control unit 400 shown in FIG. 1 has a function of controlling theheater 330, the coil 350, and the light emission unit 211. In thisembodiment, the control unit 400 is constituted by an integrated circuit(IC) chip. The control unit 400 includes an excitation light controlunit 410 that controls frequencies of the resonance light beams 1 and 2of the light emission unit 211, a temperature control unit 420 thatcontrols the temperature of an alkali metal in the gas cell 310, and amagnetic field control unit 430 that controls a magnetic field to beapplied to the gas cell 310.

The excitation light control unit 410 controls frequencies of theresonance light beams 1 and 2 emitted from the light emission unit 211on the basis of detection results of the light detection unit 320mentioned above. More specifically, the excitation light control unit410 controls the frequencies of the resonance light beams 1 and 2emitted from the light emission unit 211 so that a frequency difference(ω1−ω2) is set to a frequency ω0 inherent in the alkali metal, on thebasis of the detection results of the light detection unit 320.

Although not shown in the drawing, the excitation light control unit 410includes a voltage-controlled quartz crystal oscillator (oscillationcircuit) and outputs an oscillation frequency of the voltage-controlledquartz crystal oscillator as an output signal of the atomic oscillator100 while synchronizing and adjusting the oscillation frequency on thebasis of the detection results of the light detection unit 320. Inaddition, the temperature control unit 420 controls electricalconduction to the heater 330 on the basis of detection results of thetemperature sensor 340. Thus, it is possible to maintain the gas cell310 within a desired temperature range. In addition, the magnetic fieldcontrol unit 430 controls electrical conduction to the coil 350 so thata magnetic field generated by the coil 350 becomes constant.

As shown in FIG. 5, the heat transmission unit 360 is disposed outsidethe gas cell 310. The heat transmission unit 360 is formed of a materialhaving a thermal conductivity higher than that of at least the magneticshield 380, and transmits heat generated from the heater 330 to the gascell 310. Meanwhile, in this specification, a state where heat can betransmitted between members is referred to as a “thermally connected”state. That is, a description will be given on the assumption thatmembers are in a “thermally connected” state as long as heat can betransmitted between the members even when the members are in a contactstate or a non-contact state (for example, a state where the members arefixed using an adhesive or the like).

FIG. 6 is a perspective view showing the exterior of the heattransmission unit 360. As shown in FIG. 6, the heat transmission unit360 is constituted by a base portion 360 a having a quadrilateral plateshape when seen from the Y-axis direction on the assumption that theY-axis direction is a thickness direction, and wall portions 360 b, 360c, 360 d, and 360 e as four gas cell accommodating walls that areerected in the Y (+) direction from an edge portion of the base portion360 a. The wall portion 360 b and the wall portion 360 d face each otherin the X-axis direction. The wall portion 360 b is positioned on the X(+) side, and the wall portion 360 d is positioned on the X (−) side. Inaddition, the wall portion 360 c and the wall portion 360 e face eachother in the Z-axis direction. The wall portion 360 c is positioned onthe Z (−) side, and the wall portion 360 e is positioned on the Z (+)side. Adjacent wall portions of the wall portions 360 b, 360 c, 360 d,and 360 e are connected to each other, thereby forming a cylindricalshape as a whole. In addition, a portion surrounded by the base portion360 a and the wall portions 360 b, 360 c, 360 d, and 360 e is configuredas a first concave portion 360 f serving as a gas cell accommodationportion into which a portion of the gas cell 310 is inserted.

In addition, a second concave portion 360 g is formed at the end on theY (−) side in the base portion 360 a so as to circulate. As also shownin FIG. 5, the second concave portion 360 g is a portion in which thecoil 350 wound around the outer circumferences of each of the heattransmission unit 360 and the light absorbing unit 370 is disposed. Aportion of the coil 350 is disposed in the second concave portion 360 g,and thus it is possible to achieve a reduction in the size of the atomicoscillator 100. Meanwhile, in the heat transmission unit 360 accordingto this embodiment, a description is given of a configuration in whichthe wall portions 360 b, 360 c, 360 d, and 360 e are formed to have aframe shape, but the invention is not limited thereto. The wall portions360 b, 360 c, 360 d, and 360 e may not be connected to each other aslong as the wall portions can accommodate the gas cell 310.

In addition, the wall portion 360 b is provided with a window portion360 h which is a through hole as an opening corresponding to atransmission region of the excitation light LL in the window portion312, and the wall portion 360 d is provided with a window portion 360 jwhich is a through hole as an opening corresponding to a transmissionregion of the excitation light LL in the window portion 313. The windowportions 360 h and 360 j overlap each other so as to be able to transmitthe excitation light LL (see FIG. 5) when seen from the X-axisdirection. Accordingly, the excitation light LL passes through orpenetrates the window portion 360 h, the window portions 312 and 313 ofthe gas cell 310, and the window portion 360 j in this order in a statewhere the gas cell 310 is inserted into the first concave portion 360 f,and thus it is possible to make the excitation light LL incident on thelight detection unit 320.

Now, heat transmission performed from the heater 330 through the heattransmission unit 360 mentioned above to the gas cell 310 will bedescribed. As shown in FIG. 5, heat Q generated by the heater 330 isfirst transmitted to the heat transmission plate 390. The heat Q istransmitted to the entire heat transmission plate 390 by the heattransmission plate 390 having a high thermal conductivity, and the heatQ transmitted to the heat transmission plate 390 is transmitted andmoved toward the wall portion 380 b facing the heater 330 of themagnetic shield 380 connected to the heat transmission plate 390.

Subsequently, the heat Q transmitted to the wall portion 380 b of themagnetic shield 380 is transmitted to the heat transmission unit 360 ina state where the heat changes to heat Q1 transmitted from the end onthe Y (−) side of the base portion 360 a of the heat transmission unit360 and heat Q2 transmitted from the outer circumferential surface ofthe base portion 360 a. The heat Q1 and Q2 transmitted to the baseportion 360 a is transmitted through the heat transmission unit 360, andis partially transmitted and moved to each of the wall portions 360 b,360 c, 360 d, and 360 e. The heat Q1 and Q2 having reached each of thewall portions 360 b, 360 c, 360 d, and 360 e is transmitted to the gascell 310 as follows.

First, the heat is transmitted, as heat Q3, from the base portion 360 ato the main body 311 of the gas cell 310 connected to the bottom of thefirst concave portion 360 f (see FIG. 6). Heat other than the heat Q3transmitted to the gas cell 310 is transmitted to the wall portions 360b, 360 c, 360 d, and 360 e, and is transmitted to the window portions312 and 313 of the gas cell 310 as heat Q4 and Q5.

As described above, the gas cell 310 is inserted into the first concaveportion 360 f of the heat transmission unit 360. At this time, in orderto enable the gas cell 310 to be inserted into the first concave portion360 f, it is necessary to provide a gap δh1 between the first concaveportion 360 f and the gas cell 310 as a design condition inconsideration of variations during manufacturing. A reduction in thesize of the gas cell 310 becomes essential in the atomic oscillator 100desired to have a small size when the gas cell 310 is manufactured so asto have an external shape which is even slightly larger than the innershape of the first concave portion 360 f in a case where the gap δh1 isnot provided in design. As a result, the main body 311 of the gas cell310 or the window portions 312 and 313 are formed of a thinner material.Further, as described above, the main body 311 and the window portions312 and 313 are formed using a so-called brittle material such as glass,and thus tend to be damaged or broken due to a slight stress.

Therefore, it is necessary to provide the gap δh1 from a design stage.Here, δh1 is expressed by an expression of δh1=δh11+δh12 on theassumption that a gap between the wall portion 360 b and the windowportion 312 of the gas cell 310 in the X-axis direction shown in FIG. 5is δh11 and a gap between the wall portion 360 d and the window portion313 of the gas cell 310 is δh12, and expressions of 0≤δh11≤δh1 and0≤δh12≤δh1 are established.

In the case of a transmission path of the heat Q4 shown in FIG. 5, theheat Q4 is transmitted from the wall portions 360 b and 360 d throughthe gaps δh11 and δh12 to the window portions 312 and 313 of the gascell 310. In this case, gas, such as air, in a gas environment in thevicinity of the gas cell 310 is present in the gaps δh11 and δh12. Theair has an extremely low thermal conductivity as is well known, ratherhas a heat insulation property. Therefore, in order to transmit heatfrom the heat transmission unit 360 to the gas cell 310 whilesuppressing a heat transmission loss, heat transmission members 511 and512 as thermal conductive elastic members are mounted in the gaps δh11and δh12.

A cross-section of a portion taken along line A-A′ shown in FIG. 5 isshown in FIG. 7. As shown in FIG. 7, in addition to the gaps δh11 andδh12 mentioned above, a gap δh21 and a gap δh22 are also respectivelyset between the wall portion 360 c and the gas cell 310 and between thewall portion 360 e and the gas cell 310 in the Z-axis direction.Assuming that a gap in the Z-axis direction in a design stage is δh2,expressions of δh2=δh21+δh22, 0≤δh21≤δh2, and 0≤δh22≤δh2 areestablished.

The heat transmission member 511 is mounted in the gap δh11, the heattransmission member 512 is mounted in the gap δh12, a heat transmissionmember 513 is mounted in the gap δh21, and a heat transmission member514 is mounted in the gap δh22. A material having elasticity and thermalconductivity, for example, silicon rubber, a metal filler-containingrubber, or the like is preferably used for the heat transmission members511, 512, 513, and 514. That is, in order to transmit heat from the wallportions 360 b, 360 c, 360 d, and 360 e through the heat transmissionmembers 511, 512, 513, and 514 to the gas cell 310, the heattransmission members 511, 512, 513, and 514 can efficiently perform heattransmission by bringing the wall portions 360 b, 360 c, 360 d, and 360e and the gas cell 310 into close contact with each other. Therefore,the heat transmission members 511, 512, 513, and 514 have elasticity,and thus can normally operate to press the wall portions 360 b, 360 c,360 d, and 360 e and the gas cell 310 and can bring the wall portionsand the gas cell into close contact with each other.

In this manner, a loss of heat transmission performed from the wallportions 360 b, 360 c, 360 d, and 360 e through the heat transmissionmembers 511, 512, 513, and 514 to the gas cell 310 is reduced as shownby a heat transmission path of the heat Q5 indicated by arrows in FIG. 5by the heat transmission members 511, 512, 513, and 514 being provided,and thus it is possible to efficiently supply heat.

The light absorbing unit 370 is disposed outside the gas cell 310 asshown in FIG. 5. The light absorbing unit 370 is formed of a materialhaving a thermal conductivity higher than that of at least the magneticshield 380, and a surplus amount of heat in the gas cell 310 is radiatedto the outside of the magnetic shield 380 through the magnetic shield380.

FIG. 8 is a perspective view showing an exterior of the light absorbingunit 370. As shown in FIG. 8, the light absorbing unit 370 can beconstituted by a base portion 370 a having a quadrilateral plate shapewhen seen from the Y-axis direction on the assumption that the Y-axisdirection is a thickness direction, and four wall portions 370 b, 370 c,370 d, and 370 e serving as gas cell accommodating walls erected fromthe edge of the base portion 370 a in the Y (−) direction. The wallportion 370 b and the wall portion 370 d face each other in the Z-axisdirection. The wall portion 370 b is positioned on the Z (+) side, andthe wall portion 370 d is positioned on the Z (−) side. In addition, thewall portion 370 c and the wall portion 370 e face each other in theX-axis direction. The wall portion 370 c is positioned on the X (+)side, and the wall portion 370 e is positioned on the X (−) side.Adjacent wall portions of the wall portions 370 b, 370 c, 370 d, and 370e are connected to each other, thereby forming a cylindrical shape as awhole. In addition, a portion surrounded by the base portion 370 a andthe wall portions 370 b, 370 c, 370 d, and 370 e is configured as afirst concave portion 370 f serving as a gas cell accommodation portioninto which a portion of the gas cell 310 is inserted. Meanwhile, in thelight absorbing unit 370 according to this embodiment, a description isgiven of a configuration in which the wall portions 370 b, 370 c, 370 d,and 370 e are formed to have a frame shape, but the invention is notlimited thereto. The wall portions 370 b, 370 c, 370 d, and 370 e maynot be connected to each other as long as the wall portions canaccommodate the gas cell 310.

In addition, a second concave portion 370 g is formed in an end of thebase portion 370 a on the Y (+) side along the X-axis and is formed inouter ends of the wall portion 370 c and the wall portion 370 e alongthe Y-axis direction. As also shown in FIG. 5, the second concaveportion 370 g is a portion in which the coil 350 wound around the outercircumferences of the heat transmission unit 360 and the light absorbingunit 370 is disposed. A portion of the coil 350 is disposed in thesecond concave portion 370 g, and thus it is possible to achieve areduction in the size of the atomic oscillator 100.

In addition, a through hole 370 h having the protrusion portion 311 b ofthe gas cell 310 inserted thereinto is formed in the base portion 370 a.Heat of the protrusion portion 311 b inserted into the through hole 370h is transmitted to the light absorbing unit 370 through an innercircumferential surface of the through hole 370 h. Therefore, theprotrusion portion 311 b is prompted to be cooled by the protrusionportion 311 b being inserted into the through hole 370 h of the lightabsorbing unit 370, and a surplus portion of alkali atoms in the gascell 310 tends to condense within the liquid reserving portion 311 c ofthe protrusion portion 311 b, thereby allowing the atomic oscillator 100to be stably oscillated. Meanwhile, the through hole 370 h may be aconcave portion having an opening on the first concave portion 370 fside. In this case, the through hole has a depth that does not interferewith the protrusion portion 311 b.

Heat transmission performed from the gas cell 310 through the lightabsorbing unit 370 mentioned above to the outside of the magnetic shield380 will be described. As shown in FIG. 5, the heat Q generated by theheater 330 is transmitted to the heat transmission plate 390, the heattransmission unit 360, the heat transmission members 511, 512, 513, and514, and the gas cell 310, and the temperature of the gas cell 310 ismaintained to a desired temperature. However, the temperature of the gascell 310 may rise beyond a desired temperature in an externalenvironment at an installation location of the atomic oscillator 100,particularly, in a high temperature environment.

A unit that absorbs surplus heat from the gas cell 310 of which thetemperature has risen and radiates the heat to the outside of themagnetic shield 380 through the magnetic shield 380 is the lightabsorbing unit 370. Although the surplus heat of the gas cell 310 istransmitted to the light absorbing unit 370, the gas cell 310 isinserted into the first concave portion 370 f of the light absorbingunit 370, similar to the heat transmission unit 360.

First, the heat is transmitted, as heat Q6, from the main body 311 ofthe gas cell 310 connected to the bottom of the first concave portion370 f (see FIG. 8) to the base portion 370 a. Heat other than the heatQ6 transmitted from the gas cell 310 to the light absorbing unit 370 istransmitted to the wall portions 370 b, 370 c, 370 d, and 370 e, and istransmitted to the light absorbing unit 370 as heat Q7 and Q8.

At this time, in order to enable the gas cell 310 to be inserted intothe first concave portion 370 f, it is necessary to provide a gap δc1between the first concave portion 370 f and the gas cell 310 as a designcondition in consideration of variations during manufacturing. Areduction in the size of the gas cell 310 becomes essential in theatomic oscillator 100 desired to have a small size when the gas cell 310is manufactured so as to have an external shape which is even slightlylarger than the inner shape of the first concave portion 370 f in a casewhere the gap δc1 is not provided in design. As a result, the main body311 of the gas cell 310 or the window portions 312 and 313 are formed ofa thinner material. Further, as described above, the main body 311 andthe window portions 312 and 313 are formed using a so-called brittlematerial such as glass, and thus tend to be damaged or broken due to aslight stress.

Therefore, it is necessary to provide the gap δc1 from a design stage.Here, δc1 is expressed by an expression of δc1=δc11+δc12 on theassumption that a gap between the wall portion 370 b and the windowportion 312 of the gas cell 310 in the X-axis direction shown in FIG. 5is δc11 and a gap between the wall portion 370 d and the window portion313 of the gas cell 310 is δc12, and expressions of 0≤δc11≤δc1 and0≤δc12≤δc1 are established.

In the case of a transmission path of the heat Q7 shown in FIG. 5, theheat Q7 is transmitted from the window portions 312 and 313 of the gascell 310 through the gaps δc11 and δc12 to the wall portions 370 b and370 d. In this case, gas, such as air, in a gas environment in thevicinity of the gas cell 310 is present in the gaps δc11 and δc12. Theair has an extremely low thermal conductivity as is well known, ratherhas a heat insulation property. Therefore, in order to transmit heatfrom the gas cell 310 to the light absorbing unit 370 while suppressinga heat transmission loss, heat transmission members 611 and 612 asthermal conductive elastic members are mounted in the gaps δc11 andδc12.

A cross-section of a portion taken along line B-B′ shown in FIG. 5 isshown in FIG. 9. As shown in FIG. 9, in addition to the gaps δc11 andδc12 mentioned above, a gap δc21 and a gap δc22 are also respectivelyset between the wall portion 370 c and the gas cell 310 and between thewall portion 370 e and the gas cell 310 in the Z-axis direction.Assuming that a gap in the Z-axis direction in a design stage is δc2,expressions of δc2=δc21+δc22, 0≤δc21≤δc2, and 0≤δc22≤δc2 areestablished.

The heat transmission member 611 is mounted in the gap δc11, the heattransmission member 612 is mounted in the gap δc12, a heat transmissionmember 613 is mounted in the gap δc21, and a heat transmission member614 is mounted in the gap δc22. A material having elasticity and thermalconductivity, for example, silicon rubber, a metal filler-containingrubber, or the like is preferably used for the heat transmission members611, 612, 613, and 614. That is, in order to transmit heat from the gascell 310 through the heat transmission members 611, 612, 613, and 614 tothe wall portions 370 b, 370 c, 370 d, and 370 e, the heat transmissionmembers 611, 612, 613, and 614 can efficiently perform heat transmissionby bringing the gas cell 310 and the wall portions 370 b, 370 c, 370 d,and 370 e into close contact with each other. Therefore, the heattransmission members 611, 612, 613, and 614 have elasticity, and thusthe heat transmission members 611, 612, 613, and 614 can normallyoperate to press the wall portions 370 b, 370 c, 370 d, and 370 e andthe gas cell 310 to thereby bring the wall portions and the gas cellinto close contact with each other.

In this manner, a loss of heat transmission performed from the gas cell310 through the heat transmission members 611, 612, 613, and 614 to thewall portions 370 b, 370 c, 370 d, and 370 e is reduced as shown by aheat transmission path of the heat Q8 indicated by arrows in FIG. 5 bythe heat transmission members 611, 612, 613, and 614 being provided, andthus it is possible to efficiently supply heat.

In addition, the protrusion portion 311 b provided in the main body 311of the gas cell 310 is inserted into the through hole 370 h of the lightabsorbing unit 370, and heat Q9 is transmitted from the protrusionportion 311 b through the inner circumferential surface of the throughhole 370 h to the light absorbing unit 370. In this manner, heattransmitted from the gas cell 310 through each of the paths of the heatQ6, Q7, Q8, and Q9 to the light absorbing unit 370 is transmitted fromthe light absorbing unit 370 to the magnetic shield 380 in a state wherethe heat changes to heat Q10, and the heat is radiated to the outside ofthe magnetic shield 380. Surplus heat of the gas cell 310 is removed,and the temperature of the gas cell 310 is maintained to a predeterminedtemperature, thereby allowing the atomic oscillator 100 having astabilized oscillation property to be obtained.

FIG. 10 is a schematic diagram showing inner temperature distribution ofthe gas cell 310 included in the atomic oscillator 100 shown in FIG. 5along line C-C′. As shown in FIG. 10, the heat transmission unit 360 andthe light absorbing unit 370 are disposed so as to face each other inthe Y-axis direction through the gas cell 310. The amount of gas cell310 inserted into the first concave portion 360 f of the heattransmission unit 360 and the first concave portion 370 f of the lightabsorbing unit 370 (see FIGS. 6 and 8) is set so as to separate the wallportions 360 b, 360 c, 360 d, and 360 e of the heat transmission unit360 and the wall portions 370 b, 370 c, 370 d, and 370 e of the lightabsorbing unit 370 from each other, and a separation distance H isprovided.

It is possible to prevent heat from being directly transmitted from theheat transmission unit 360 to the light absorbing unit 370 by providingthe separation distance H. A region of gas such as air is formed betweenthe wall portions 360 b, 360 c, 360 d, and 360 e of the heattransmission unit 360 and the wall portions 370 b, 370 c, 370 d, and 370e of the light absorbing unit 370 by further separating the wallportions from each other, and it is possible to make the region operateas a heat insulating portion. In addition, the wall portions 360 b, 360c, 360 d, and 360 e of the heat transmission unit 360 and the inner wallof the magnetic shield 380 form a space portion J. In the space portionJ, gas such as air functions as a heat insulating member, and it ispossible to prevent heat from moving from the wall portions 360 b, 360c, 360 d, and 360 e of the heat transmission unit 360 to the magneticshield 380 and to suppress a loss of heat transmission from the heattransmission unit 360 to the gas cell 310.

The temperature distribution of the gas cell 310 can be maintained to apredetermined temperature Ts at which a desired number of alkali metalatoms can be present in a transmission region of the excitation lightLL, that is, in a region Dh which is covered by the wall portions 360 b,360 c, 360 d, and 360 e of the heat transmission unit 360 by heat fromthe heater 330 which is transmitted from the wall portions 360 b, 360 c,360 d, and 360 e of the heat transmission unit 360 as shown in FIG. 10.

However, in a case where surplus alkali metal atoms are present in thegas cell 310, for example, the alkali metal atoms may condense on thewindow portions 312 and 313 of the gas cell 310, which leads to aconcern for interference with the transmission of the excitation lightLL. Consequently, the surplus alkali metal atoms are condensed in aregion within the gas cell 310 other than the transmission region of theexcitation light LL to thereby stabilize the number of alkali metalatoms in the transmission region of the excitation light LL, and thusthe light absorbing unit 370 for forming a condensation region isprovided.

In a region Dd, having a separation distance H, which is adjacent to theregion Dh covered by the wall portions 360 b, 360 c, 360 d, and 360 e ofthe heat transmission unit 360 in which a predetermined temperature Tsis maintained, heat is radiated from the gas cell 310 to a space portionformed between the wall portions 360 b, 360 c, 360 d, and 360 e of theheat transmission unit 360 and the wall portions 370 b, 370 c, 370 d,and 370 e of the light absorbing unit 370, and thus the temperaturefalls by t1 from the predetermined temperature Ts.

Further, in a Dc1 region covered by the wall portions 370 b, 370 c, 370d, and 370 e of the light absorbing unit 370, the wall portions 370 b,370 c, 370 d, and 370 e of the light absorbing unit 370 absorb heat fromthe gas cell 310 as described above, and thus the temperature falls byt2. Thereby, the Dc1 region covered by the wall portions 370 b, 370 c,370 d, and 370 e of the light absorbing unit 370 is formed as acondensation region for a surplus portion of the alkali metal atoms.

In addition, in a Dc2 region surrounded by the through hole 370 h of thelight absorbing unit 370 into which the protrusion portion 311 bprovided in the main body 311 of the gas cell 310 is inserted, heat isfurther transmitted from the protrusion portion 311 b through thethrough hole 370 h to the light absorbing unit 370, and the temperaturefurther falls by t3 than in the Dc1 region, thereby allowing a surplusportion of the alkali metal atoms to be condensed and held in the liquidreserving portion 311 c.

The above-mentioned atomic oscillator 100 shown in FIG. 5 is configuredsuch that four heat transmission members 511, 512, 513, and 514 aredisposed in respective gaps between the gas cell 310 and the wallportions 360 b, 360 c, 360 d, and 360 e of the heat transmission unit360, but is not limited thereto. FIGS. 11 to 14 are cross-sectionalviews showing other configurations of the heat transmission members 511,512, 513, and 514 disposed in respective gaps of the gas cell 310 shownin FIG. 7 and the wall portions 360 b, 360 c, 360 d, and 360 e of theheat transmission unit 360, and are diagrams equivalent to a crosssection of the portion taken along the line A-A′ shown in FIG. 5.

As shown in FIG. 11, a heat transmission member 521 that presses the gascell 310 toward the wall portion 360 d of the heat transmission unit 360in the X (−) direction and a heat transmission member 522 that pressesthe gas cell 310 toward the wall portion 360 e of the heat transmissionunit 360 in the Z (+) direction may be provided. As shown in FIG. 11, ina case where the heat transmission members 521 and 522 are disposed, aportion of the external surface of the gas cell 310 is in direct contactwith the wall portion 360 e or the wall portion 360 d, thereby securingthermal connection therebetween.

In a configuration shown in FIG. 7, four components of the heattransmission members 511, 512, 513, and 514 are disposed in the gapsδh11, δh12, δh21, and δh22 formed by the gas cell 310 and the wallportions 360 b, 360 c, 360 d, and 360 e of the heat transmission unit360. However, as shown in FIG. 12, a heat transmission member 530 havinga so-called packing configuration in which the heat transmission members511, 512, 513, and 514 are integrally formed may be adopted. In thismanner, it is possible to achieve thermal connection between the gascell 310 and the wall portions 360 b, 360 c, 360 d, and 360 e of theheat transmission unit 360 without an interval by using the integralheat transmission member 530.

In a configuration shown in FIG. 13, a heat transmission member 541 isdisposed between the wall portion 360 b of the heat transmission unit360 and the window portion 312 of the gas cell 310 in the X-axisdirection, and a heat transmission member 542 is disposed between thewall portion 360 d of the heat transmission unit 360 and the windowportion 313 of the gas cell 310. In other words, the heat transmissionmembers 541 and 542 are interposed between the wall portions 360 b and360 d of the heat transmission unit 360 which are disposed so as to facethe gas cell 310 in the X-axis direction. In addition, in aconfiguration shown in FIG. 14, one window portion 313 of the gas cell310 in the X-axis direction is directly thermally connected to the wallportion 360 d of the heat transmission unit 360, and a heat transmissionmember 550 is disposed between the other window portion 312 and the wallportion 360 b of the heat transmission unit 360.

According to the arrangement of the heat transmission members 541, 542,and 550 shown in FIGS. 13 and 14, although not shown in the drawing,heat is transmitted from the wall portions 360 b and 360 d of the heattransmission unit 360 to the gas cell 310 in a direction along theoptical axis of the excitation light LL shown in FIG. 5, that is, alongthe X-axis. Therefore, it is possible to effectively heat a transmissionregion along the optical axis of the excitation light LL even with asmaller number of heat transmission members and to stabilize oscillationcharacteristics of the atomic oscillator 100.

Although described above, the heat transmission members 511, 512, 513,and 514 shown in FIG. 7, the heat transmission members 521 and 522 shownin FIG. 11, and the heat transmission member 530 shown in FIG. 12 areformed to have a sheet shape using an elastic member having a thermalconductivity, for example, silicon rubber, and thus the members can beinterposed between the gas cell 310 and the wall portions 360 b, 360 c,360 d, and 360 e of the heat transmission unit 360. In addition, arubber-based filler having a thermal conductivity and elasticity bycoagulation may be filled between the gas cell 310 and the wall portions360 b, 360 c, 360 d, and 360 e of the heat transmission unit 360 and maybe then coagulated.

Other configurations of the arrangement of the heat transmission membersin the heat transmission unit 360 have been described. Similarly, in thelight absorbing unit 370, heat transmission members (heat transmissionmembers 611, 612, 613, and 614 shown in FIG. 9) may have arrangementconfigurations shown in FIGS. 11 to 14, similar to the heat transmissionunit 360.

Second Embodiment

As a second embodiment, a positioning system using a GPS satellite willbe described as an example of an electronic apparatus including theatomic oscillator 100 according to the first embodiment. FIG. 15 is adiagram showing a schematic configuration in a case where the atomicoscillator according to the invention is used for the positioning systemusing a GPS satellite.

A positioning system 1000 shown in FIG. 15 includes a GPS satellite1100, a base station device 1200, and a GPS reception device 1300. TheGPS satellite 1100 transmits positioning information (GPS signal). Thebase station device 1200 includes a reception device 1202 that receivespositioning information from the GPS satellite 1100 with a high level ofaccuracy through an antenna 1201 installed, for example, at anelectronic reference point (GPS continuous observation station), and atransmission device 1204 that transmits the positioning information,which is received by the reception device 1202, through an antenna 1203.

Here, the reception device 1202 is an electronic device including theatomic oscillator 100 mentioned above of the first embodiment accordingto the invention as the reference frequency oscillation source thereof.The reception device 1202 has excellent reliability. In addition, thepositioning information received by the reception device 1202 istransmitted by the transmission device 1204 in real time. The GPSreception device 1300 includes a satellite reception unit 1302 thatreceives positioning information from the GPS satellite 1100 through anantenna 1301, and a base station reception unit 1304 that receivespositioning information from the base station device 1200 through anantenna 1303.

Third Embodiment

As a third embodiment, a clock transmission system will be described asan example of an electronic apparatus including the atomic oscillator100 according to the first embodiment. FIG. 16 is a diagram showing aschematic configuration in a case where the atomic oscillator accordingto the invention is used for a clock transmission system.

A clock transmission system 2000 shown in FIG. 16 conforms clocks ofrespective devices within a network of a time division multiplex systemto each other, and is a system having a redundant configuration of anormal (N) system and an emergency (E) system.

The clock transmission system 2000 includes a clock supply module (CSM)2001 and a synchronous digital hierarchy (SDH) device 2002 of an Astation (upper (N system)), a clock supply module 2003 and an SDH device2004 of a B station (upper (E system)), and a clock supply module 2005and SDH devices 2006 and 2007 of a C station (lower). The clock supplymodule 2001 includes an atomic oscillator 100, and generates a clocksignal of the N system. The atomic oscillator 100 in the clock supplymodule 2001 generates a clock signal in synchronization with a moreaccurate clock signal applied from master clocks 2008 and 2009 includingan atomic oscillator using cesium.

The SDH device 2002 performs the transmission and reception of a mainsignal on the basis of a clock signal applied from the clock supplymodule 2001, superimposes the clock signal of the N system on the mainsignal, and transmits the superimposed signals to the lower clock supplymodule 2005. The clock supply module 2003 includes an atomic oscillator100 and generates a clock signal of the E system. The atomic oscillator100 in the clock supply module 2003 generates a clock signal insynchronization with a more accurate clock signal applied from themaster clocks 2008 and 2009 including an atomic oscillator using cesium.

The SDH device 2004 performs the transmission and reception of a mainsignal on the basis of a clock signal applied from the clock supplymodule 2003, superimposes the clock signal of the E system on the mainsignal, and transmits the superimposed signals to the lower clock supplymodule 2005. The clock supply module 2005 receives clock signals appliedfrom the clock supply modules 2001 and 2003, and generates a clocksignal in synchronization with the received clock signal.

Here, the clock supply module 2005 normally generates a clock signal insynchronization with the clock signal of the N system which is appliedfrom the clock supply module 2001. In a case where an abnormality occursin the N system, the clock supply module 2005 generates a clock signalin synchronization with the clock signal of the E system which isapplied from the clock supply module 2003. Switching from the N systemto the E system is performed in this manner, and thus it is possible tosecure stable clock supply and to increase the reliability of a clockpath network. The SDH device 2006 performs the transmission andreception of a main signal on the basis of the clock signal applied fromthe clock supply module 2005. Similarly, the SDH device 2007 performsthe transmission and reception of a main signal on the basis of theclock signal applied from the clock supply module 2005. Thereby, it ispossible to synchronize the module of the C station with the module ofthe A station or the B station.

Fourth Embodiment

As a fourth embodiment, a vehicle will be described as an example of amoving object including the atomic oscillator 100 according to the firstembodiment. FIG. 17 is a perspective view showing a schematicconfiguration in a case where the atomic oscillator according to theinvention is used for the vehicle as a moving object.

A vehicle 3000 as a moving object shown in FIG. 17 includes a vehiclebody 3001 and four wheels 3002, and is configured to rotate the wheels3002 by a power source, not shown in the drawing, which is provided inthe vehicle body 3001. The vehicle 3000 has the atomic oscillator 100built therein. For example, a control unit not shown in the drawingcontrols the driving of the power source on the basis of an oscillationsignal applied from the atomic oscillator 100.

Meanwhile, an electronic apparatus or a moving object having the atomicoscillator according to the invention incorporated therein are notlimited to the above-mentioned apparatus or moving object, and can beapplied to, for example, a mobile phone, a digital still camera, an inkjet type discharge apparatus (for example, an inkjet printer), apersonal computer (a mobile personal computer and a laptop type personalcomputer), a television, a video camera, a video tape recorder, a carnavigation apparatus, a pager, an electronic organizer (an electronicorganizer with a communication function is also included), an electronicdictionary, an electronic calculator, an electronic game machine, a wordprocessor, a workstation, a video phone, a television monitor forsecurity, electronic binoculars, a POS terminal, medical equipment (forexample, an electronic thermometer, a sphygmomanometer, a blood sugarmeter, an electrocardiographic measurement device, an ultrasonicdiagnostic apparatus, and an electronic endoscope), a fish detector,various measurement apparatuses, instruments (for example, instrumentsfor vehicles, aircraft, and ships), a flight simulator, and the like.

As described above, the atomic oscillator according to the invention hasbeen described with reference to the accompanying drawings, but theinvention is not limited thereto. For example, a configuration of eachunit in the above-described embodiment can be replaced with anyconfiguration exhibiting the same function, and can also have anyconfiguration added thereto. In addition, the invention may have acombination of any configurations of the above-described embodiments.

What is claimed is:
 1. An atomic oscillator comprising: a gas cell thatis configured with a pair of window members and a wall so that the gascell has an inner space enclosed by the pair of window members and thewall, the pair of window members being opposite to each other, metalatoms being sealed in the inner space, the wall having first, second,third, and fourth side frames, the third and fourth side frames beingconnected between the first and second side frames, the first, second,third, and fourth frames being connected to the pair of window members;a heater configured to heat the gas cell, the heater being provided at aside directly adjacent to the first side frame of the gas cell; a heattransmission member that is coupled to the first, third, and fourth sideframes and part of the pair of window members so as to thermally connectthe heater to the gas cell and to transmit heat generated by the heaterto the gas cell; a heat absorbing member that is coupled to the second,third, and fourth side frames and part of the pair of window members soas to be thermally connected to the gas cell and to absorb heat of thegas cell and dissipate the heat to an outside of the gas cell; a firstthermal conductive elastic member configured to transfer heat, the firstthermal conductive elastic member being provided between the heattransmission member and a first outer surface of the gas cell so thatthe first thermal conductive elastic member is sandwiched therebetween,the first outer surface is configured with the first, third, and fourthside frames and the part of the pair of window members; and a secondthermal conductive elastic member configured to transfer heat, thesecond thermal conductive elastic member being provided between the heatabsorbing member and a second outer surface of the gas cell so that thesecond thermal conductive elastic member is sandwiched therebetween, thesecond outer surface is configured with the second, third, and fourthside frames and the part of the pair of window members, wherein the heatgenerated by the heater transmits to the heat absorbing member via theheat transmission member, the first thermal conductive elastic member,the gas cell, and the second thermal conductive elastic member.
 2. Theatomic oscillator according to claim 1, wherein each of the first andsecond thermal conductive elastic members is a rubber-based adhesive, apacking, or a sheet piece.
 3. The atomic oscillator according to claim1, wherein each of the first and second thermal conductive elasticmembers is a rubber-based filler.
 4. The atomic oscillator according toclaim 1, further comprising: a coil that generates a magnetic fieldpassing through the gas cell; and a magnetic shield that accommodatesthe gas cell, the heat transmission member, the heat absorbing member,and the coil therein, wherein the heat transmission member and the heatabsorbing member are thermally connected to the magnetic shield, andwherein the heater is thermally connected to an outer side of themagnetic shield.